Inflating tires with N2 has a few real and some theoretical advantages. However many of the sales claims are based on the assumption that the vehicle owner never monitors or maintains tire inflation.
The issue come up when facts are considered. Tires inflated with "AIR" have about 78% N2. Under test conditions 3 years later due to normal out-gassing of the O2 and addition of more air a tire will end up with about 82 to 85% N2.
Most shops offering N2 are not using pure bottled N2 but are using a nitrogen separator so are creating a gas that is about 98 - 99% N2. When you inflate a tire with 99% you do not end up with 99 as there is O2 left in the tire originally and even a 3x fill and purge does not remove all the O2 so you end up with about 94-96% N2.
Cost If there was no cost I would say do it but there is a cost both direct payment to dealer and sometimes additional travel time & cost to dealer location.
pay-back Doubtful as MPG is theoretical and probably may not even measurable if all performance characteristics are considered. Tire life may also be doubtful since most RV tires are replaced due to age.
